title: Epidemiological and molecular aspects of rifampicin-resistant Staphylococcus aureus isolated from wounds, blood and respiratory samples.
abstract: OBJECTIVE
  To study the incidence of rifampicin-resistant Staphylococcus aureus in Gipuzkoa, Northern Spain, and to characterize representative resistant isolates and mutations associated with resistance.
  
  
  METHODS
  For rifampicin-resistant isolates, the rpoB gene fragment that includes the most frequent mutations conferring rifampicin resistance in S. aureus was amplified and sequenced. The role of new mutations responsible for rifampicin resistance was confirmed by cloning and complementation in trans. Resistant isolates were characterized by multilocus sequence typing and PFGE.
  
  
  RESULTS
  Between 1999 and 2008, 0.59% (96/16 348) of S. aureus clinical isolates studied showed rifampicin resistance. Rifampicin resistance was higher in methicillin-resistant S. aureus (MRSA) than in methicillin-susceptible S. aureus (MSSA) (3.26% versus 0.26%; P < 0.001). Twenty-two randomly selected rifampicin-resistant isolates were studied in depth, 11 showing low-level and 11 showing high-level rifampicin resistance (rifampicin MICs of 2-4 mg/L and ≥8 mg/L, respectively). Overall, 12 different mutations in the rpoB gene were detected, including a newly described N474K mutation followed by the insertion of a glycine residue at position 475. Among the eight different sequence types (STs) found, the most frequent were ST8 and ST863, the latter being associated with respiratory infections. Ten of the 11 low-level rifampicin-resistant isolates were MRSA ST8 and had the same H481N mutation, while the 11 high-level rifampicin-resistant isolates, 6 MSSA and 5 MRSA, belonged to eight different STs and had distinct rpoB mutations.
  
  
  CONCLUSIONS
  Low-level rifampicin-resistant isolates were mainly clonal while high-level resistant isolates showed a high genetic diversity. Most mutations observed coincided with those found in other studies, but a new mutation conferring rifampicin resistance was detected.
authors.affiliation: Microbiology Service Hospital Donostia, San Sebastián, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Villar
authors.forename: José M
authors.initials: JM
authors.lastname: Marimón
authors.forename: José M
authors.initials: JM
authors.lastname: García-Arenzana
authors.forename: Adela G
authors.initials: AG
authors.lastname: de la Campa
authors.forename: María J
authors.initials: MJ
authors.lastname: Ferrándiz
authors.forename: Emilio
authors.initials: E
authors.lastname: Pérez-Trallero
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D016470:Bacteremia / Q000453:epidemiology* / Q000382:microbiology; D015373:Bacterial Typing Techniques; D002648:Child; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000235:genetics; D004351:Drug Resistance; D016521:Electrophoresis, Gel, Pulsed-Field; D005260:Female; D005816:Genetic Complementation Test; D005838:Genotype; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D058885:Multilocus Sequence Typing; D011110:Polymorphism, Genetic; D012141:Respiratory Tract Infections / Q000453:epidemiology* / Q000382:microbiology; D012293:Rifampin / Q000494:pharmacology*; D017422:Sequence Analysis, DNA; D013030:Spain / Q000453:epidemiology; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D014946:Wound Infection / Q000453:epidemiology* / Q000382:microbiology; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D012321:DNA-Directed RNA Polymerases; C105078:RNA polymerase beta subunit; D012293:Rifampin